I did quick scans of the forum and google, but couldn't find what I was looking for, so I thought I'd ask here.

Does anyone know how to capture PPP traffic from a cellphone AirCard Modem?

I'm trying to troubleshoot an issue that someone is having with VPN, and thought a packet capture via Wireshark would be helpful here.

The problem is, the box I'm using to test on has to get it's connection via a USB Aircard from a cell phone provider. WinPcap sees it as PPP traffic on Windows 7 and doesn't capture the data according to there FAQ.

When I looked at connecting my laptops and nokia n800 in the past, it was less an issue with the hardware, and more an issue with the software they use for tracking your traffic usage. I was able to do it between my phone and nokia in the past (different carrier). I could probably find how to do the same with the aircard. But I needed to test out the connection from a windows box. part of it was testing the profile I had.

Most devices will begin between 1 and 3 which cannot be sniffed by outside devices as there is no IP going on yet. In order to see what occurs during the setup, you'd need to be in the path of the cellular and device doing the ppp transaction(s). You mention nokia, you can get a sniffer on that device and do some capturing to see what happens.

Now *after the ppp connection* (between 4 and 6) you would need to be somewhere sniffing either on the ppp device or through some insane port mirroring or other. Otherwise AFTER the fact, you're seeing IP (IPCP or IPE, etc). What you may be able to do is mirror the ppp server where the phone would go through the ppp setup by connecting to you first:

In this setup, it would help to sniff on a, c and e. This way you can compare and see who is doing what, where and at which stage. Otherwise the data you may need to see (on the original ASCII diagram) 2,3,4 would never be seen unless you have something to decapsulate the ppp frames.

Sil. We got off in the weeds... My comments about noikas were a rebuttal to eth3real's driver comment.

I was trying to find a way to capture the data in steps 4 - 6, to make sure that there wasn't a problem with the VPN Server (client / server).

Bit of an explanation on the original problem:I set up a new vpn profile for a customer. but when ever the customer would try to connect he would get an immediate error response saying unknown problem at peer.

I needed to be logged in on my work laptpp, and was using my netbook as a test device using a verizon air card. I was getting the same error as the client when trying to connect. I wanted to see what the traffic looked like, to see if the problem was the pcf file, or on the server side. make sure that things were trying to establish and get a baseline to troubleshoot with to compare my side vs the customer's side.

And it all had to be done through Windows.

In the end, the whole thing ended up being a mess, and we ended up going a slightly different route that's working for now. (Problem on customer's end sending UDP traffic).

Last edited by rattis on Thu Oct 20, 2011 12:03 pm, edited 1 time in total.

chrisj wrote:I was trying to find a way to capture the data in steps 4 - 6, to make sure that there wasn't a problem with the VPN Server (client / server).

In the end, the whole thing ended up being a mess, and we ended up going a slightly different route that's working for now. (Problem on customer's end sending UDP traffic).

Unf... VPN diagnosing is a PITA big time. Whenever I have to debug on say Juniper SSGs or better, I always want to pull my hair out since each side of a tunnel usually has to have every parameter EXACT.

You say UDP and in the initial post, I saw PPP,, are you doing L2TP? If so, I hope its L2TP over IPSEC, remember, L2TP doesn't encrypt if you didn't know this already. Reason for me asking is, I have a client in NYC, set up his own "tunnels" using L2TP alone where everything and its mother was sniffable.